Method for producing aqueous acrylamide solution

ABSTRACT

There is provided a method for producing an aqueous acrylamide solution by reacting a composition including acrylonitrile with water to produce acrylamide, in which the composition including acrylonitrile includes 3 to 15 mg of propionitrile per 1 kg of the total weight of the composition including acrylonitrile. According to the present invention, a production method with which it is possible to suppress acrylamide polymerization without lowering quality and thereby obtain a stable aqueous acrylamide solution can be provided.

TECHNICAL FIELD

The present invention relates to a method for producing an aqueousacrylamide solution.

The present application claims priority to Japanese Patent ApplicationNo. 2011-112428, which has been filed in Japan on May 19, 2011, which ishereby incorporated by reference in its entirety.

BACKGROUND ART

Acrylamide has many applications, such as flocculating agents, petroleumrecovering agents, paper strength enhancers in the paper producingindustry, and thickeners for papermaking, and is a useful substance as araw material for polymers.

Among industrial processes for acrylamide production, used long time agois a sulfuric acid hydrolysis process which consists of the step ofheating acrylonitrile together with sulfuric acid and water to obtain anaqueous solution of acrylamide sulfate salts. This process has then beenreplaced with a copper-catalyzed process in which acrylonitrile isreacted with water in the presence of a copper catalyst (for example,metal copper, reduced copper, Raney copper, or the like) to obtain anaqueous solution of acrylamide. In addition, in recent years, as aproduction process with fewer by-products, industrial production basedon a biocatalyst method is also carried out as a biocatalyst method forobtaining an aqueous solution of acrylamide by using a biocatalyst suchas nitrile hydratase derived from microorganisms (for example, PatentDocuments 1 to 4).

As in the case of many unsaturated monomers, acrylamide is easy topolymerize by the action of light or heat and also has a property ofvery easily polymerizing particularly upon contact with the surface ofiron, so that an aqueous solution of acrylamide has been difficult tostably handle since the polymerization of acrylamide easily occursduring each step of its production or during its preservation.

A method of using various stabilizers has been proposed as a method forstabilization by suppressing polymerization of acrylamide. Examples ofthe stabilizers include thiourea, ammonium rhodanide, nitrobenzol(Patent Document 5), ferron (Patent Document 6), furil dioxime (PatentDocument 7), cyanide complex compound of chromium (Patent Document 8),p-nitrosodiphenyl hydroxyamine (Patent Document 9), and so on. Thosestabilizers are used for preventing polymerization during a process ofproducing acrylamide or for stabilization of an aqueous solution ofacrylamide.

CITATION LIST Patent Document

-   Patent Document 1: JP 56-17918 B-   Patent Document 2: JP 59-37951 B-   Patent Document 3: JP 02-470 A-   Patent Document 4: WO 2009/113654 A-   Patent Document 5: JP 39-10109 B-   Patent Document 6: JP 40-7171 B-   Patent Document 7: JP 40-7172 B-   Patent Document 8: JP 41-1773 B-   Patent Document 9: JP 45-11284 B

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

The stabilizers described above all correspond to polymerizationinhibitors. Stabilizers with a small stabilizing effect, that is,polymerization inhibiting effect, have problems of reduced quality ofacrylamide, such as discoloration and reduced purity of acrylamide,because they should be added in large amounts to acrylamide. On theother hand, stabilizers with a high polymerization inhibiting effect mayadversely affect the polymerization operations during production ofacrylamide polymers such as having a difficulty to obtain desired highmolecular weight polymers or reduced polymerization rate, even when usedin small amounts.

The present invention is devised in view of the above circumstances, andan object of the present invention is to provide a production methodwith which it is possible to suppress acrylamide polymerization withoutlowering quality, and thereby obtain a stable aqueous acrylamidesolution.

Means for Solving Problem

As a result of intensive studies to solve the problems stated above, theinventors of the present invention have found that when acrylamide isproduced from acrylonitrile containing a predetermined amount ofpropionitrile, polymerization of acrylamide during its production andpreservation can be suppressed without lowering the quality ofacrylamide to thereby significantly improve its stability, and thepresent invention is completed accordingly.

The present invention has following aspects.

[1] A method for producing an aqueous acrylamide solution by reactingacrylonitrile with water to produce acrylamide, in which acrylonitrilecontaining 3 to 15 mg/kg of propionitrile is used as the acrylonitrile.

[2] The method for producing an aqueous acrylamide solution described in[1], in which the reaction with water is performed in the presence of abiocatalyst.

[3] The method for producing an aqueous acrylamide solution described in[1] or [2], in which the acrylonitrile also contains 2 to 20 mg/kg ofacetonitrile.

[4] The method for producing an aqueous acrylamide solution described inany one of [1] to [3], in which the concentration of the acrylamide inthe aqueous acrylamide solution is 30 to 60% by mass.

Specifically, the present invention relates to the followings.

[1] A method for producing an aqueous acrylamide solution includingreacting a composition containing acrylonitrile with water to produceacrylamide, in which the composition containing acrylonitrile contains 3to 15 mg of propionitrile per 1 kg of the total weight of thecomposition containing acrylonitrile.

[2] The method for producing an aqueous acrylamide solution described in[1], in which the method includes performing the reaction of thecomposition containing acrylonitrile with water in the presence of abiocatalyst.

[3] The method for producing an aqueous acrylamide solution described in[1] or [2], in which the composition containing acrylonitrile alsocontains 2 to 20 mg/kg of acetonitrile per 1 kg of the total weight ofthe composition containing acrylonitrile.

[4] The method for producing an aqueous acrylamide solution described inany one of [1] to [3], in which the concentration of the acrylamide inthe aqueous acrylamide solution is 30 to 60% by mass relative to thetotal mass of the aqueous acrylamide solution.

Effect of the Invention

According to the production method of the present invention, a stableaqueous acrylamide solution is obtained as polymerization of acrylamidecan be suppressed without lowering the quality.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described. Thefollowing embodiments are merely examples provided for illustrating thepresent invention, and the present invention is not intended to belimited thereto. The present invention may be carried out in variousembodiments without departing from the spirit of the present invention.

All publications cited in this specification, including technicalliteratures, patent laid-open publications, patent publications andother patent documents, are incorporated herein by reference in theirentirety.

The present invention relates to a method for producing an aqueousacrylamide solution by reacting acrylonitrile with water to produceacrylamide. Examples of the method of reacting acrylonitrile with waterinclude a sulfuric acid hydration process which is the process forearlier industrial production of acrylamide, a copper-catalyzed processwhich is a current major process for industrial production, and abiocatalyst process which is recently industrialized, and any method canbe used. By using specific acrylonitrile for the reaction with water, astabilizing effect of suppressing polymerization of acrylamide to beproduced can be obtained with any method. Further, the aqueousacrylamide solution to be obtained has favorable quality, and thereforea negative influence on a polymerization process for producing anacrylamide polymer is also not exhibited.

The composition containing acrylonitrile that is used in the presentinvention is a mixture of acrylonitrile and propionitrile; or a mixtureof acrylonitrile, propionitrile, and acetonitrile.

The composition containing acrylonitrile that is used in the presentinvention contains 3 to 15 mg/kg, and preferably 5 to 10 mg/kg ofpropionitrile per 1 kg of the total weight of the composition containingacrylonitrile. When acrylamide is produced by reacting a compositioncontaining acrylonitrile in which propionitrile content is less than 3mg per 1 kg of the total weight of the composition containingacrylonitrile with water, the stabilizing effect of suppressingpolymerization of acrylamide is hardly obtained. On the other hand, whenthe propionitrile content is more than 15 mg per 1 kg of the totalweight of the composition containing acrylonitrile, the stabilizingeffect is lowered.

In acrylonitrile as a raw material (that is, the composition containingacrylonitrile according to the present invention), propionitrile isgenerally present as impurities.

When the propionitrile content in acrylonitrile as a raw material (forexample, commercially available acrylonitrile or acrylonitrilesynthesized by a method known in the field) has a desired value, the rawmaterial can be directly used for the reaction with water.

When the propionitrile content in acrylonitrile as a raw material islower than a desired value, it is possible to add propionitrile to theraw material to have a desired value. As for the propionitrile to beadded, commercially available propionitrile may be used or propionitrilesynthesized by a method known in the field may be used. When theaddition amount of propionitrile is extremely tiny amount relative toacrylonitrile, a diluted propionitrile liquid may be also added for easyaddition. At that time, as for the liquid for dilution, water may beused. However, when a decrease in the concentration of acrylonitrilecaused by addition of diluted propionitrile liquid is not desirable, itis possible that propionitrile is diluted in acrylonitrile at a desiredconcentration and the diluted liquid is added to acrylonitrile.

When the propionitrile content in acrylonitrile as a raw material ishigher than a desired value, propionitrile can be removed bypurification of the raw material. Examples of the purification methodfor removing propionitrile in a composition containing acrylonitrileinclude rectification. Rectification of the composition containingacrylonitrile can be carried out by a known method, for example, by amethod described in JP 2010-222309 A.

Adjustment of the propionitrile content in the composition containingacrylonitrile may be also carried out by mixing a composition containingacrylonitrile which contains propionitrile at high content (for example,higher than 15 mg/kg) and a composition containing acrylonitrile whichcontains propionitrile at low content (for example, lower than 3 mg/kg).By adjusting the propionitrile content in each composition containingacrylonitrile, their mixing ratio, or the like, desired propionitrilecontent can be obtained.

It is preferable that the composition containing acrylonitrile that isused in the present invention also contain 2 to 20 mg, and preferably 5to 15 mg/kg of acetonitrile per 1 kg of the total weight of thecomposition containing acrylonitrile. When acrylamide is produced byreacting a composition containing acrylonitrile in which acetonitrilecontent is at least 2 mg/kg per 1 kg of the total weight of thecomposition containing acrylonitrile with water, the stabilizing effectof suppressing polymerization of acrylamide is enhanced. On the otherhand, when the acetonitrile content is more than 20 mg per 1 kg of thetotal weight of the composition containing acrylonitrile, thestabilizing effect may be lowered.

Similar to propionitrile, acetonitrile is generally present asimpurities in acrylonitrile as a raw material (that is, the compositioncontaining acrylonitrile according to the present invention).

Adjustment of the acetonitrile content in the composition containingacrylonitrile may be carried out in the same manner as propionitrile.

Each of the propionitrile content and the acetonitrile content in thecomposition containing acrylonitrile can be measured by gaschromatography mass analysis, liquid chromatography mass analysis, orthe like.

As for the method of reacting acrylamide with water in the presentinvention, a biocatalyst method is preferable in that acrylamide withhigh purity can be obtained with fewer reaction by-products. Thebiocatalyst method is a method of producing acrylamide by reactingacrylonitrile with water in the presence of a biocatalyst, and it isdescribed in many literatures, for example, JP 56-17918 B, JP 59-37951B, JP 02-470 A, and WO 2009/113654 A. In the present invention, exceptthat a specific acrylonitrile is used for the reaction with water, aknown method can be used.

Herein, the biocatalyst includes animal cells, plant cells, cellorganelles, cell bodies of microorganisms (cell bodies of living or deadmicroorganisms) or treated products thereof, which contain an enzymecatalyzing a desired reaction (that is, nitrile hydratase).

Such treated products include an enzyme (that is, crude or purifiedenzyme) extracted from the animal cells, plant cells, cell organelles,cell bodies of microorganisms; or animal cells, plant cells, cellorganelles, cell bodies of microorganisms, or enzymes themselves whichare immobilized on a carrier; or the like.

Examples of the method for immobilization include entrapping,cross-linking, and carrier binding. Entrapping refers to a technique bywhich cell bodies of microorganisms or enzymes are enclosed within afine lattice of polymer gel or coated with a semipermeable polymermembrane. Cross-linking refers to a technique by which enzymes arecross-linked with a reagent having two or more functional groups (thatis, a multifunctional cross-linking agent). Furthermore, carrier bindingrefers to a technique by which enzymes are bound to a water insolublecarrier.

Examples of a carrier (that is, an immobilization carrier) for use inimmobilization include glass beads, silica gel, polyurethane,polyacrylamide, polyvinyl alcohol, carrageenan, alginic acid, agar andgelatin.

Cell bodies of microorganisms or treated products thereof areparticularly preferable as a biocatalyst.

Examples of the above microorganisms include microorganisms belonging tothe genus Nocardia, genus Corynebacterium, genus Bacillus, genusPseudomonas, genus Micrococcus, genus Rhodococcus, genus Acinetobacter,genus Xanthobacter, genus Streptomyces, genus Rhizobium, genusKlebsiella, genus Enterobacter, genus Erwinia, genus Aeromonas, genusCitrobacter, genus Achromobacter, genus Agrobacterium and genusPseudonocardia, or the like.

Production of an aqueous acrylamide solution using a biocatalyst may becarried out by a continuous reaction, by which acrylamide is produced ina continuous manner, or by batch reaction, by which acrylamide isproduced in a non-continuous manner. Although not limited thereto, it ispreferably carried out by continuous reaction.

When a continuous reaction is carried out, an aqueous acrylamidesolution is produced in a continuous manner without collecting theentire reaction mixture in the reactor while maintaining continuous orintermittent supply of raw materials for reaction (containing abiocatalyst, water as a raw material, and acrylonitrile) to the reactorand continuous or intermittent recovery of the reaction mixture(containing the produced acrylamide) from the reactor.

When a batch reaction is carried out, an aqueous acrylamide solution isproduced by reaction after supplying an entire amount of the rawmaterials for reaction to the reactor or by reaction with continuous orintermittent supply of remaining part of the raw materials for reactionto the reactor after injecting part of the raw materials for reaction tothe reactor.

As for the type of the reactors, reactors of various types such asstirring tank type, fixed bed type, fluid bed type, moving bed type,tubular type, or tower type may be used. It is possible that only onereactor is used or plural reactors are used in combination. When pluralreactors are used in combination, concentration of the recoveredacrylamide in a reaction mixture is higher at a downstream side. Forsuch reasons, based on the number of the reactors, concentration ofacrylamide in an aqueous acrylamide solution that is finally obtainedcan be controlled.

When continuously performing a reaction using plural reactors, thereactor into which the biocatalyst and acrylonitrile are to be suppliedis not limited to the most upstream reactor, and the materials may alsobe introduced into a reactor downstream thereof, as long as it is withina range in which efficiency of the reaction or the like are not impairedtoo much.

Among the raw materials for reaction, water as a raw material is usedfor the reaction of acrylonitrile with water for producing acrylamide.Examples of the water as a raw material include water; or an aqueoussolution containing acids or salts that are dissolved in water. Examplesof the acids include phosphoric acid, acetic acid, citric acid, andboric acid. Examples of the salts include sodium slat, potassium salt,and ammonium salt of the acids. Specific examples of the water as a rawmaterial include, although not particularly limited thereto, pure water,tap water, tris buffer solution, phosphate buffer solution, acetatebuffer solution, citrate buffer solution, and borate buffer solution. pHof the water as a raw material is preferably between 5 and 9 (25° C.).

Although the use amount of the biocatalyst may vary depending on thetype and form of the biocatalyst to be used, it is preferably adjustedsuch that the activity of the biocatalyst to be introduced into areactor is around 50 to 500 U per mg of dried cell bodies ofmicroorganisms at a reaction temperature of 10° C. The above unit “U(unit)” is intended to mean that one micromole of acrylamide is producedfor one minute from acrylonitrile, which is measured by usingacrylonitrile to be used for production.

Although the use amount of the composition containing acrylonitrile mayvary depending on the type and form of the biocatalyst to be used, it ispreferably adjusted such that the acrylonitrile concentration in the rawmaterials for reaction is around 0.5% to 15.0% by mass with respect tothe raw materials for reaction.

The reaction temperature (that is, temperature of the reaction mixture)is, although not particularly limited, preferably 10 to 50° C., and morepreferably 20 to 40° C. When the reaction temperature is at least 10°C., reaction activity of the biocatalyst can be sufficiently increased.Further, when the reaction temperature is 40° C. or lower, deactivationof the biocatalyst can be easily suppressed.

The reaction time is, although not particularly limited, preferably 1 to50 hours, and more preferably 3 to 30 hours.

When production of the aqueous acrylamide solution is carried out bycontinuous reaction, fluid rate at the time of collecting the reactionmixture from the reactor is determined based on addition rate ofacrylonitrile and the biocatalyst such that the production can be madein a continuous manner without collecting the entire reaction mixture inthe reactor.

For the purpose of facilitating stabilization, at least one watersoluble monocarboxylic acid salt containing two or more carbon atoms maybe added to the raw materials for the reaction used for the reaction ofacrylonitrile with water or to the reaction mixture during or after thereaction with water.

The water soluble monocarboxylic acid salt may be any one of a salt of asaturated monocarboxylic acid or a salt of an unsaturated monocarboxylicacid. Examples of the saturated carboxylic acid include acetic acid,propionic acid, and n-caproic acid. Examples of the unsaturatedcarboxylic acid include acrylic acid, methacrylic acid, and vinyl aceticacid. Typical salts are sodium salts, potassium salts, and ammoniumsalts.

Addition amount of the water soluble monocarboxylic acid is preferablyan amount which is 20 to 5000 mg/kg as an acid relative to acrylamide inthe reaction mixture (aqueous acrylamide solution) that is finallyobtained.

In the present invention, acrylamide concentration in the aqueousacrylamide solution is preferably 30 to 60% by mass, more preferably 35to 55% by mass, and still more preferably 40 to 50% by mass relative tothe total weight of the aqueous acrylamide solution.

If the acrylamide concentration is higher than 60% by mass, crystals ofacrylamide may easily precipitate near ambient temperature and hence aheating apparatus is required, so that not only facility costs will beincreased, but also temperature control and other operations will becomplicated. For such reasons, the concentration of the aqueousacrylamide solution of the present invention is, for example, preferably60% by mass or less, more preferably 55% by mass or less, and mostpreferably 50% by mass or less, although it is not particularly limitedas long as it is within the range where crystals of acrylamide will notprecipitate even near ambient temperature.

Meanwhile, if the acrylamide concentration is lower than 30% by mass, itis economically disadvantageous from the industrial standpoint becausethe tank volume used for storage or keeping will be excessively large ortransport costs will also be increased. Thus, the acrylamideconcentration in the aqueous acrylamide solution is, for example,preferably 30% by mass or more, more preferably 35% by mass or more, andmost preferably 40% by mass or more.

The acrylamide concentration in the aqueous acrylamide solution can beadjusted by concentration of acrylonitrile in the raw materials for thereaction, type or shape of the biocatalyst to be used, or the reactioncondition (that is, reaction temperature, reaction time, or number ofthe reactor) or the like.

It is believed that, in the aqueous acrylamide solution obtained byreacting acrylonitrile containing a predetermined amount ofpropionitrile with water, propionitrile or its reaction product withwater is contained. However, there is almost no bad influence on thepolymerization (for example, difficulty in obtaining a polymer withdesired high molecular weight, decreased polymerization rate, or thelike). Thus, the aqueous acrylamide solution obtained by the productionmethod of the present invention can be directly subjected, depending onthe use thereafter, to a polymerization process to obtain a desiredacrylamide polymer.

EXAMPLES

The present invention will be further described in more detail by way ofthe following examples, but the present invention is not limited tothem.

Meanwhile, in each example described below, “%” represents “% by mass”,unless specifically described otherwise.

As for the pH, values at 25° C. were measured by a glass electrodemethod.

Example 1 Preparation of Biocatalyst

Rhodococcus rhodochrous J1 strain having nitrile hydratase activity(Accession number: PERM BP-1478; internationally deposited toInternational Patent Organism Depositary, National Institute of AdvancedIndustrial Science and Technology (Chuo 6, Higashi 1-1-1, Tsukuba-shi,Ibaraki, Japan) on Sep. 18, 1987) was aerobically cultured in a mediumcontaining 2% glucose, 1% urea, 0.5% peptone, 0.3% yeast extract and0.05% cobalt chloride (pH 7.0) at 30° C. Using a centrifuge and 50 mMphosphate buffer (pH 7.0), the obtained culture was subjected to harvestand washing, thereby preparing a bacterial cell suspension as abiocatalyst (dried cell bodies: 15% by mass).

(Adjustment of Propionitrile Concentration)

Propionitrile concentration and acetonitrile concentration inacrylonitrile (hereinbelow, “acrylonitrile A”) manufactured byDia-Nitrix Co., Ltd. were analyzed by gas chromatography (column: fusedsilica capillary No. 55 DB-225, column length: 25 m, oven temperature:temperature was increased from 50° C. to 200° C., detector temperature:250° C., carrier gas: helium, split ratio: 1/50, detector: FID, andinjection amount: 0.6 μL). As a result, in the acrylonitrile A,propionitrile concentration was 1 mg/kg and acetonitrile concentrationwas 1 mg/kg.

By adding 0.1 g of propionitrile (manufactured by Kanto Chemical Co.,Inc., purity of 99%) to 99 g of acrylonitrile A, 0.1% dilutedpropionitrile liquid was prepared. Next, by adding 0.20 g of the 0.1%diluted propionitrile liquid to 100 g of the acrylonitrile A,acrylonitrile in which propionitrile concentration was 3 mg/kg andacetonitrile concentration was 1 mg/kg was obtained (hereinbelow,“acrylonitrile B”).

(Reaction from Acrylonitrile to Acrylamide)

With the following method, acrylonitrile B was reacted with water toobtain an aqueous acrylamide solution.

Reactors equipped with a jacket having internal volume of 1 L (internaldiameter of 10 cm) were connected in series to have seven tanks. To thefirst tank, 50 mM phosphate buffer solution (pH 7) was added at 780mL/hr, the acrylonitrile B was added at 214 mL/hr, and suspension of thecell bodies were added at 2.0 g/hr in a continuous manner. To the secondtank, only the acrylonitrile B was added at 182 mL/hr in a continuousmanner. To the third tank, only the acrylonitrile B was added at 133mL/hr in a continuous manner, and to the fourth tank, only theacrylonitrile B was added at 55 mL/hr in a continuous manner. Each tankwas all subjected to stirring. The reaction temperature was controlledby using jacket cooling water (10° C.) such that the liquid temperatureof the first tank to the seventh tank becomes 24, 24, 25, 26, 27, 28,and 28° C., respectively.

One day later, the reaction liquid discharged from the seventh tank wasanalyzed by gas chromatography (column: manufactured by Waters,PoraPak-PS, 1 m, 180° C., carrier gas: helium, detector: FID). As aresult, only acrylamide was detected and non-reacted acrylonitrile wasnot detected. Acrylamide concentration in the reaction liquid was 50%.

(Evaluation of Stability of Aqueous Acrylamide Solution)

The aqueous acrylamide solution was taken in an amount of 30 g andintroduced into a 50 mL polypropylene container (a product of AS ONECorporation, under the trade name of Ai-Boy wide-mouth bottle).

A stainless washer (SUS304, inner diameter: 9 mm, outer diameter: 18 mm)was washed with acetone and then with pure water, followed by drying.After drying, the washer was introduced into the 50 mL polypropylenecontainer containing the aqueous acrylamide solution. This polypropylenecontainer was held in a thermostat kept at 70° C. to measure the numberof days required until the acrylamide in the aqueous acrylamide solutionis polymerized (that is, until a pop corn-like polymerized product wasproduced).

As a result, the pop corn-like polymerized product was produced after 15days.

Example 2

By adding 1.01 g of propionitrile (manufactured by Kanto Chemical Co.,Inc., purity of 99%) to 99 g of acrylonitrile A, 1% dilutedpropionitrile liquid was prepared. Next, by adding 0.14 g of the 1%diluted propionitrile liquid to 100 g of the acrylonitrile A,acrylonitrile in which propionitrile concentration is 15 mg/kg andacetonitrile concentration is 1 mg/kg was obtained (hereinbelow,“acrylonitrile C”). The acrylonitrile C was reacted with water in thesame order as Example 1 to obtain an aqueous acrylamide solution.

Stability of the obtained aqueous acrylamide solution was evaluated inthe same order as Example 1. As a result, a pop corn-like polymerizedproduct was produced after 21 days.

Example 3

By adding 0.01 g of acetonitrile (manufactured by Kanto Chemical Co.,Inc., purity of 99%) to 99.9 g of acrylonitrile B, 0.01% dilutedacetonitrile liquid was prepared. Next, by adding 1.02 g of the 0.01%diluted acetonitrile liquid to 100 g of the acrylonitrile B,acrylonitrile in which propionitrile concentration was 3 mg/kg andacetonitrile concentration was 2 mg/kg was obtained (hereinbelow,“acrylonitrile D”). The acrylonitrile D was reacted with water in thesame order as Example 1 to obtain an aqueous acrylamide solution.

Stability of the obtained aqueous acrylamide solution was evaluated inthe same order as Example 1. As a result, a pop corn-like polymerizedproduct was produced after 35 days.

Example 4

By adding 0.2 g of acetonitrile (manufactured by Kanto Chemical Co.,Inc., purity of 99%) to 99 g of acrylonitrile B, 0.2% dilutedacetonitrile liquid was prepared. Next, by adding 0.96 g of the 0.2%diluted acetonitrile liquid to 100 g of the acrylonitrile B,acrylonitrile in which propionitrile concentration was 3 mg/kg andacetonitrile concentration was 20 mg/kg was obtained (hereinbelow,“acrylonitrile E”). The acrylonitrile E was reacted with water in thesame order as Example 1 to obtain an aqueous acrylamide solution.

Stability of the obtained aqueous acrylamide solution was evaluated inthe same order as Example 1. As a result, a pop corn-like polymerizedproduct was produced after 38 days.

Example 5

By adding 1.47 g of the 0.2% diluted acetonitrile liquid prepared inExample 4 to 100 g of the acrylonitrile B, acrylonitrile in whichpropionitrile concentration was 3 mg/kg and acetonitrile concentrationwas 30 mg/kg was obtained (hereinbelow, “acrylonitrile F”). Theacrylonitrile F was reacted with water in the same order as Example 1 toobtain an aqueous acrylamide solution.

Stability of the obtained aqueous acrylamide solution was evaluated inthe same order as Example 1. As a result, a pop corn-like polymerizedproduct was produced after 14 days.

Comparative Example 1

The acrylonitrile A was reacted with water in the same order as Example1 to obtain an aqueous acrylamide solution.

Stability of the obtained aqueous acrylamide solution was evaluated inthe same order as Example 1. As a result, a pop corn-like polymerizedproduct was produced after 3 days.

Comparative Example 2

By adding 0.19 g of the 1% diluted propionitrile liquid prepared inExample 2 to 100 g of the acrylonitrile A, acrylonitrile in whichpropionitrile concentration was 20 mg/kg and acetonitrile concentrationwas 1 mg/kg was obtained (hereinbelow, “acrylonitrile G”). Theacrylonitrile G was reacted with water in the same order as Example 1 toobtain an aqueous acrylamide solution.

Stability of the obtained aqueous acrylamide solution was evaluated inthe same order as Example 1. As a result, a pop corn-like polymerizedproduct was produced after 6 days.

TABLE 1 Number of days Propionitrile Acetonitrile required forconcentration in concentration in polymerization of acrylonitrileacrylonitrile acrylamide [mg/kg] [mg/kg] [Days] Example 1 3 1 15 Example2 15 1 21 Example 3 3 2 35 Example 4 3 20 38 Example 5 3 30 14Comparative 1 1 3 example 1 Comparative 20 1 6 example 2

As described in the above results, by reacting acrylonitrile containing3 to 15 mg/kg of propionitrile, polymerization of the acrylamide can besuppressed during storage so that the stability of the aqueousacrylamide solution can be significantly improved.

In addition, as a result of evaluating the appearance of the aqueousacrylamide solution (that is, presence or absence of coloration), thepolymerization rate at the time of producing an acrylamide polymer, andthe molecular weight of the obtained acrylamide polymer or the like,favorable results were obtained from all of them, and no reduction inquality of the aqueous acrylamide solution was exhibited.

INDUSTRIAL APPLICABILITY

According to the present invention, an aqueous acrylamide solution canbe conveniently stabilized without lowering quality of acrylamide.Therefore, the present invention is useful as a method for preventingpolymerization of acrylamide during production, storage and/or transportof the aqueous acrylamide solution.

1. A method for producing an aqueous acrylamide solution, the methodcomprising reacting a composition comprising acrylonitrile and water toproduce acrylamide, wherein the composition further comprises 3 to 15 mgof propionitrile per 1 kg of the total weight of the composition.
 2. Themethod according to claim 1, wherein the reacting occurs in the presenceof a biocatalyst.
 3. The method according to claim 1, wherein thecomposition further comprises 2 to 20 mg/kg of acetonitrile per 1 kg ofthe total weight of the composition.
 4. The method according to claim 1,wherein a concentration of the acrylamide in the aqueous acrylamidesolution is 30 to 60% by mass relative to the total mass of the aqueousacrylamide solution.
 5. The method according to claim 2, wherein thecomposition further comprises 2 to 20 mg/kg of acetonitrile per 1 kg ofthe total weight of the composition.
 6. The method according to claim 2,wherein a concentration of the acrylamide in the aqueous acrylamidesolution is 30 to 60% by mass relative to the total mass of the aqueousacrylamide solution.
 7. The method according to claim 3, wherein aconcentration of the acrylamide in the aqueous acrylamide solution is 30to 60% by mass relative to the total mass of the aqueous acrylamidesolution.